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> Switching Power Supplies, Spurous Radiations
cgriggs
Posted: June 05, 2017 08:59 pm
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I bought a Motorola Police radio that was converted to 2 meters for our repeater from our local ham club. (Very popular unit in the group!) I didn't have a power supply heavy enough to be able to transmit, but it received well.

I then looked up 12 volt switching supplies on ebay. I found one, sent for it and when it came, I hooked it up.

Judas Priest!! My 40 meter receiver went nuts. Fanning the dial made me find that it didn't obliterate everything, but when I hit the mike button the receiver was drowned out. Probably just overloaded.

Do I have to get a MC battery and junk the power supply, or what? Is there a fix?
I'll eventually find what the ones here with their Motorolas did, but I'm hoping to have a solution here before I have to ask.

Charlie
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Sch3mat1c
Posted: June 05, 2017 09:48 pm
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Well, eBay, what were you expecting... wacko.gif

You can try to filter it, putting LC filters on all the (input and output) lines, and putting the whole thing inside a box (ground all the filters to the box, so nothing goes through the bulkhead without being filtered). You can take some shortcuts (using CM chokes and 'X' and 'Y' caps as appropriate), but this is the surest way to filter it if you don't know what shortcuts to take.

Otherwise, purchase a new power supply that actually has data listed from a recognized test lab. It might still need filtering, mind -- you are talking about radios right nearby, not just neighborhood noise pollution. But it won't need as much.

Caveat emptor -- this is one illustration of why they put those little marks on there. So you know what you're buying when you need those specs. smile.gif

Oh, and I'd put external fuses on that thing, too, just in case it's not fused properly... (I wouldn't trust it any further than I can throw it, and I have weedy girl arms, if that gives you any idea about that!) wink.gif

Tim


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MacFromOK
Posted: June 05, 2017 10:10 pm
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QUOTE (Sch3mat1c @ June 05, 2017 03:48 pm)
(I wouldn't trust it any further than I can throw it, and I have weedy girl arms, if that gives you any idea about that!) wink.gif

Huh. I always thought the word was "reedy," but maybe it depends on what yer smokin' ...
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dmg
Posted: June 05, 2017 11:04 pm
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i dunno what are your power requirements, but if you need a clean powersource than use a battery.. 12 volt seems quite easy to get i guess.
or if that does not suit you, why not get a non switch mode powersupply ?
depending on what current you require, a 2nd hand traditional (i.e. non switchmode) battery charger will be happy to serve i think. or you can get a transformator, and build a regulator. a linear one.
ferrite beads, X and Y caps and inductors where allready listed above, you can go fancy and have those and a decent reservoir capacitor bank just in case.

for a really short cut you may wish to try it with an atx psu, its not the best thing in the world, but maybe has better noise suppression than the ebay stuff and make the thing work properly.
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cgriggs
Posted: June 06, 2017 12:19 am
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... sigh ...
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Sch3mat1c
Posted: June 06, 2017 01:07 am
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Nice thing about the battery is it's an automatic UPS. Bug --> feature? dunno.gif

Tim


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